Steep-switch field effect transistor with integrated bi-stable resistive system

ABSTRACT

Fabricating a steep-switch transistor includes receiving a semiconductor structure including a substrate, a fin disposed on the substrate, a source/drain disposed on the substrate adjacent to the fin, a gate disposed upon the fin, a cap disposed on the gate, a trench contact formed on and in contact with the source/drain, and a source/drain contact formed on an in contact with the trench contact. A recess is formed in a portion of the source/drain contact using a recess patterning process. A bi-stable resistive system (BRS) material is deposited in the recess in contact with the portion of the source/drain contact. A metallization layer is formed in contact upon the BRS material, a portion of the source/drain contact, the BRS material, and a portion of the metallization layer contact forming a reversible switch.

TECHNICAL FIELD

The present invention relates generally to a method for fabricating asteep-switch field effect transistor and an apparatus formed by themethod. More particularly, the present invention relates to a method forfabricating a steep-switch field effect transistor with an integratedbi-stable resistive system and an apparatus formed by the method.

BACKGROUND

An integrated circuit (IC) is an electronic circuit formed using asemiconductor material, such as Silicon, as a substrate and by addingimpurities to form solid-state electronic devices, such as transistors,diodes, capacitors, and resistors. Commonly known as a “chip” or a“package”, an integrated circuit is generally encased in rigid plastic,forming a “package”. The components in modern day electronics generallyappear to be rectangular black plastic packages with connector pinsprotruding from the plastic encasement. Often, many such packages areelectrically coupled so that the chips therein form an electroniccircuit to perform certain functions.

The software tools used for designing ICs produce, manipulate, orotherwise work with the circuit layout and circuit components on verysmall scales. Some of the components that such a tool may manipulate mayonly measure tens of nanometer across when formed in Silicon. Thedesigns produced and manipulated using these software tools are complex,often including hundreds of thousands of such components interconnectedto form an intended electronic circuitry.

A layout includes shapes that the designer selects and positions toachieve a design objective. The objective is to have the shape—thetarget shape—appear on the wafer as designed. However, the shapes maynot appear exactly as designed when manufactured on the wafer throughphotolithography. For example, a rectangular shape with sharp cornersmay appear as a rectangular shape with rounded corners on the wafer.

Once a design layout, also referred to simply as a layout, has beenfinalized for an IC, the design is converted into a set of masks orreticles. A set of masks or reticles is one or more masks or reticles.During manufacture, a semiconductor wafer is exposed to light orradiation through a mask to form microscopic components of the IC. Thisprocess is known as photolithography.

A manufacturing mask is a mask usable for successfully manufacturing orprinting the contents of the mask onto wafer. During thephotolithographic printing process, radiation is focused through themask and at certain desired intensity of the radiation. This intensityof the radiation is commonly referred to as “dose”. The focus and thedosing of the radiation is controlled to achieve the desired shape andelectrical characteristics on the wafer.

A Field Effect Transistor (FET) is a semiconductor device that hascontrols the electrical conductivity between a source of electriccurrent (source) and a destination of the electrical current (drain).The FET uses a semiconductor structure called a “gate” to create anelectric field, which controls the free charged carriers andconsequently the electrical conductivity of a channel between the sourceand the drain. The channel is a charge carrier pathway constructed usinga semiconductor material.

SUMMARY

The illustrative embodiments provide a method, apparatus, and computerprogram product. An embodiment of a method for fabricating asteep-switch transistor includes receiving a semiconductor structureincluding a substrate, a fin disposed on the substrate, a source/draindisposed on the substrate adjacent to the fin, a gate disposed upon thefin, a cap disposed on the gate, a trench contact formed on and incontact with the source/drain, and a source/drain contact formed on anin contact with the trench contact. The embodiment further includesforming a recess in a portion of the source/drain contact using a recesspatterning process. The embodiment further includes depositing abi-stable resistive system (BRS) material in the recess in contact withthe portion of the source/drain contact. The embodiment further includesforming a metallization layer contact upon the BRS material, a portionof the source/drain contact, the BRS material, and a portion of themetallization layer contact forming a reversible switch.

In an embodiment, forming the recess in the portion of the trenchcontact further includes applying an organic planarization layer (OPL)to mask portions of semiconductor structure, etching a portion of thesource/drain contact to form the recess therein, and removing the OPL.

In an embodiment, the BRS material comprises an insulator-to-metaltransition (IMT) material. In an embodiment, depositing the BRS materialin the recess includes depositing the IMT material in contact with theportion of the source/drain contact. An embodiment further includesremoving a portion of the IMT material outside of the recess using aplanarization process. In an embodiment, the planarization processincludes a chemical mechanical planarization (CMP) process.

In an embodiment, the BRS material comprises a threshold-switchingselector. In an embodiment, depositing the BRS material in the recessincludes depositing an oxide layer within the recess, and forming a topelectrode within the recess upon the oxide layer.

An embodiment further includes applying an insulation cap layer to thestructure, and depositing a dielectric layer upon the insulation layer,the metallization layer contact being formed through the insulation caplayer and the dielectric layer.

An embodiment of an apparatus includes a semiconductor structureincluding a substrate, a fin disposed on the substrate, a source/draindisposed on the substrate adjacent to the fin, a gate disposed upon thefin, a cap disposed on the gate, a trench contact formed on and incontact with the source/drain; and a source/drain contact formed on anin contact with the trench contact. The embodiment further includes arecess formed in a portion of the source/drain contact using a recesspatterning process. The embodiment further includes a bi-stableresistive system (BRS) material deposited in the recess in contact withthe portion of the source/drain contact. The embodiment further includesa metallization layer contact formed upon the BRS material, a portion ofthe source/drain contact, the BRS material, and a portion of themetallization layer contact forming a reversible switch.

An embodiment includes a computer usable program product. The computerusable program product includes one or more computer-readable storagedevices, and program instructions stored on at least one of the one ormore storage devices.

In an embodiment, the computer usable code is stored in a computerreadable storage device in a data processing system, and wherein thecomputer usable code is transferred over a network from a remote dataprocessing system.

In an embodiment, the computer usable code is stored in a computerreadable storage device in a server data processing system, and whereinthe computer usable code is downloaded over a network to a remote dataprocessing system for use in a computer readable storage deviceassociated with the remote data processing system.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the invention are setforth in the appended claims. The invention itself, however, as well asa preferred mode of use, further objectives and advantages thereof, willbest be understood by reference to the following detailed description ofthe illustrative embodiments when read in conjunction with theaccompanying drawings, wherein:

FIG. 1 illustrates a simplified illustration of an operating principaland dependency of a FET sub-threshold slope on key physical parameters;

FIG. 2A depicts an example conventional MOSFET structure at a MOL stageof semiconductor fabrication;

FIG. 2B depicts an example conventional MOSFET structure at a BEOL stageof semiconductor fabrication;

FIG. 3A depicts an embodiment of a SS-FET structure at a MOL stage ofsemiconductor fabrication;

FIG. 3B depicts an embodiment of a SS-FET structure at a BEOL stage ofsemiconductor fabrication;

FIG. 4 depicts example operating principles of a steep-switch FET(SS-FET) according to one or more embodiments;

FIG. 5 depicts further example operating principles of an SS-FETaccording to one or more embodiments;

FIG. 6 depict further example operating principles of an SS-FETaccording to one or more embodiments;

FIG. 7 depicts a symmetrical SS-FET architecture structure in an OFFstate and an ON state;

FIG. 8 depicts a portion of an example process for fabricating a SS-FETin accordance with an embodiment;

FIG. 9 depicts another portion of the example process for fabricating anSS-FET in accordance with an embodiment;

FIG. 10 depicts another portion of the example process for fabricatingan SS-FET in accordance with an embodiment;

FIG. 11 depicts another portion of the example process for fabricatingan SS-FET in accordance with an embodiment;

FIG. 12 depicts another portion of the example process for fabricatingan SS-FET in accordance with an embodiment;

FIG. 13 depicts another portion of the example process for fabricatingan SS-FET in accordance with an embodiment;

FIG. 14 depicts another example process for fabricating a SS-FET inaccordance with an embodiment;

FIG. 15 depicts another portion of the example process for fabricatingan SS-FET in accordance with an embodiment;

FIG. 16 depicts another portion of the example process for fabricatingan SS-FET in accordance with an embodiment;

FIG. 17 depicts another portion of the example process for fabricatingan SS-FET in accordance with an embodiment;

FIG. 18 depicts another portion of the example process for fabricatingan SS-FET in accordance with an embodiment;

FIG. 19 depicts another portion of the example process for fabricatingan SS-FET in accordance with an embodiment;

FIG. 20 depicts another portion of the example process for fabricatingan SS-FET in accordance with an embodiment;

FIG. 21 depicts a portion of another example process for fabricating anSS-FET in accordance with an embodiment;

FIG. 22 depicts another portion of the example process for fabricatingan SS-FET in accordance with an embodiment;

FIG. 23 depicts another portion of the example process for fabricatingan SS-FET in accordance with an embodiment;

FIG. 24 depicts another portion of the example process for fabricatingan SS-FET in accordance with an embodiment;

FIG. 25 depicts another portion of the example process for fabricatingan SS-FET in accordance with an embodiment;

FIG. 26 depicts another portion of the example process for fabricatingan SS-FET in accordance with an embodiment;

FIG. 27 depicts another portion of the example process for fabricatingan SS-FET in accordance with an embodiment;

FIG. 28 depicts a portion of another example process for fabricating anSS-FET in accordance with an embodiment;

FIG. 29 depicts another portion of the example process for fabricatingan SS-FET in accordance with an embodiment;

FIG. 30 depicts another portion of the example process for fabricatingan SS-FET in accordance with an embodiment;

FIG. 31 depicts another portion of the example process for fabricatingan SS-FET in accordance with an embodiment;

FIG. 32 depicts another portion of the example process for fabricatingan SS-FET in accordance with an embodiment;

FIG. 33 depicts another portion of the example process for fabricatingan SS-FET in accordance with an embodiment;

FIG. 34 depicts another portion of the example process for fabricatingan SS-FET in accordance with an embodiment;

FIG. 35 depicts another portion of the example process for fabricatingan SS-FET in accordance with an embodiment;

FIG. 36 depicts a portion of another example process for fabricating aSS-FET in accordance with an embodiment;

FIG. 37 depicts another portion of the example process for fabricatingan SS-FET in accordance with an embodiment;

FIG. 38 depicts another portion of the example process for fabricatingan SS-FET in accordance with an embodiment;

FIG. 39 depicts another portion of the example process for fabricatingan SS-FET in accordance with an embodiment;

FIG. 40 depicts another portion of the example process for fabricatingan SS-FET in accordance with an embodiment;

FIG. 41 depicts another portion of the example process for fabricatingan SS-FET in accordance with an embodiment;

FIG. 42 depicts a flowchart of an example process for fabricating asteep-switch field effect transistor in accordance with an illustrativeembodiment; and

FIG. 43, this figure depicts a flowchart of another example process forfabricating a steep-switch field effect transistor in accordance with anillustrative embodiment.

DETAILED DESCRIPTION

One or more embodiments of the present invention are directed to aprocess for fabricating a Steep-Switch Field Effect Transistor (SS-FET)having an integrated bi-stable resistive system (BRS) and an apparatusformed by the process. Conventional metal-oxide-semiconductor fieldeffect transistors (“MOSFETs”) typically have a subthreshold slope thatis thermally limited to about 60-70 mV per decade at room temperature(about 300 Kelvin). In other words, for typical FET transistors,increasing the gate voltage by about 60 mV results in a correspondingdrain current increase of less than about a factor of 10. This limitedsubthreshold slope cannot provide arbitrarily fast transitions between“OFF” (low current) and “ON” (high current) states of the FETtransistor. Accordingly, the user of conventional FETs results in atrade-off between low power and high performance.

A semiconductor fabrication process typically includes afront-end-of-line (FEOL) stage, a middle-of-the-line (MOL) stage, andback-end-of-line (BEOL) stage. Typical FEOL processes include waferpreparation, well formation, channel formation, Shallow Trench Isolation(STI) formation, gate patterning, spacer, extension implantation,Source/Drain Epitaxy formation and implantation, and silicide formation.Typical MOL processes are mainly directed to source/drain (S/D) contact(CA) formation and gate contact (CB) formation. The MOL level ofsemiconductor manufacturing includes forming local interconnects withina device. In a typical MOL stage of a manufacturing process, aninterface material, such as nickel silicide, is deposited on the source,drain, and gate of a transistor structure and contacts are then formedon top of the structures. In a typical BEOL stage of a manufacturingprocess, interconnects are formed on top of the contacts formed duringthe MOL stage to interconnect individual transistors and/or othersemiconductor devices on the wafer.

One or more embodiments of the invention provide a Steep-Switch FET(SS-FET) which leverages a Bi-Stable Resistive System (BRS)monolithically integrated on the Source and/or Drain to achievesub-thermal subthreshold slope (e.g., sub-kT/q). In other words, asubthreshold slope much less than the fundamental Boltzmann limit of 60mV per decade at room temperature is achievable. The BRS includes anymaterial or combination of materials that exhibits a unipolar, abrupt,reversible, and electrically triggered resistance switch between twostable resistance states, such as but not limited to, insulator-to-metaltransition (IMT) materials, threshold-switching selectors (TSS),resistive memories, and Spin-Transfer-Torque (STT) structures. Examplesof IMT materials include but are not limited to relaxed, strained,3D-bulk, thin film, 2D-nanosheet, 1D-nanowire such as VO₂, NbO₂,Ca₂RuO₄, LaCoC₃, Ti₂O₃, Ti₃O₅, SmNiO₃, NdNiO₃, V₂O₃, V₄O₇, Fe₃O₄, andany oxides of the form ABO₃ Perovskite. Examples of TSSs include but arenot limited to threshold-switching selectors based on a combination of athin insulation layer with a metal such as Ag/HfO₂, Cu/HfO₂, Ag/TiO₂,Cu_(x)S, Ag/a-Si, and AgTe/TiN/TiO₂/TiN.

In accordance with one or more embodiments, a steep-switch FET isachieved by monolithically integrating a Bi-stable Resistive System(BRS) on the Source and/or Drain of a FET such as a planar MOSFET,SOI-FET, Fin-FET, or Nanosheet-FET. In particular embodiments, the BRSis monolithically integrated at a MOL level of a semiconductorfabrication process. In other particular embodiments, the BRS ismonolithically integrated at a BEOL level of a semiconductor fabricationprocess.

An embodiment can be implemented as a software application. Theapplication implementing an embodiment can be configured as amodification of an existing fabrication system, as a separateapplication that operates in conjunction with an existing fabricationsystem, a standalone application, or some combination thereof. Forexample, the application causes the fabrication system to perform thesteps described herein, to fabricate SS-FET devices as described herein.

For the clarity of the description, and without implying any limitationthereto, the illustrative embodiments are described using a singleSS-FET device. An embodiment can be implemented with a different numberof SS-FETs within the scope of the illustrative embodiments.Furthermore, a transistor channel of various embodiments can have itsshape and geometrical orientation other than the ones found in theSS-FETs described herein including but not limiting to planar,surround-gate, multiple-gate, nano-wire or nano-sheet, and verticalchannels. The SS-FETs can be wired into a number of useful circuits suchas CMOS logic circuits (e.g. NAND and NOR), memory cells (e.g. SRAM),analog circuits (e.g. PLL), and input/output (I/O) circuits.

Furthermore, simplified diagrams of the example SS-FET devices are usedin the figures and the illustrative embodiments. In an actualfabrication of an SS-FET device, additional structures that are notshown or described herein may be present without departing the scope ofthe illustrative embodiments. Similarly, within the scope of theillustrative embodiments, a shown or described structure in the exampleSS-FETs may be fabricated differently to yield a similar operation orresult as described herein.

Differently shaded portions in the two-dimensional drawing of theexample SS-FETs are intended to represent different structures in theexample SS-FETs, as described herein. The different structures may befabricated using suitable materials that are known to those of ordinaryskill in the art.

A specific shape or dimension of a shape depicted herein is not intendedto be limiting on the illustrative embodiments. The shapes anddimensions are chosen only for the clarity of the drawings and thedescription and may have been exaggerated, minimized, or otherwisechanged from actual shapes and dimensions that might be used in actuallyfabricating a SS-FET according to the illustrative embodiments.

Furthermore, the illustrative embodiments are described with respect toan SS-FET only as an example. The steps described by the variousillustrative embodiments can be adapted for fabricating other planar andnon-planar devices, and such adaptations are contemplated within thescope of the illustrative embodiments.

An embodiment when implemented in a software application causes afabrication system to performs certain steps as described herein. Thesteps of the fabrication process are depicted in the several figures.Not all steps may be necessary in a particular fabrication process. Somefabrication processes may implement the steps in different order,combine certain steps, remove or replace certain steps, or perform somecombination of these and other manipulations of steps, without departingthe scope of the illustrative embodiments.

A method of an embodiment described herein, when implemented to executeon a manufacturing device, tool, or data processing system, comprisessubstantial advancement of the functionality of that manufacturingdevice, tool, or data processing system in fabricating SS-FET devices.

The illustrative embodiments are described with respect to certain typesof devices, contacts, layers, planes, structures, materials, dimensions,numerosity, data processing systems, environments, components, andapplications only as examples. Any specific manifestations of these andother similar artifacts are not intended to be limiting to theinvention. Any suitable manifestation of these and other similarartifacts can be selected within the scope of the illustrativeembodiments.

The examples in this disclosure are used only for the clarity of thedescription and are not limiting to the illustrative embodiments.Additional data, operations, actions, tasks, activities, andmanipulations will be conceivable from this disclosure and the same arecontemplated within the scope of the illustrative embodiments.

Any advantages listed herein are only examples and are not intended tobe limiting to the illustrative embodiments. Additional or differentadvantages may be realized by specific illustrative embodiments.

Furthermore, a particular illustrative embodiment may have some, all, ornone of the advantages listed above.

With reference to FIG. 1, FIG. 1 illustrates a simplified illustrationof an operating principal and dependency of a FET sub-threshold slope onkey physical parameters 100. The subthreshold slope SS of a FET may bedetermined by the following equation:

${SS} = {\left( \frac{d\;\log_{10}I_{DS}}{{dV}_{GS}} \right)^{- 1} = {\left\lbrack {\left( \frac{d\;\psi_{s}}{{dV}_{GS}} \right)\left( \frac{d\;\log_{10}I_{DS}}{d\;\psi_{s}} \right)} \right\rbrack^{- 1} \equiv {m \times n}}}$

In which I_(DS) is the drain-source current, V_(GS) is the applied gatevoltage, and ψ_(s) is the surface potential. The variable m quantifiesthe coupling capacitance between the surface potential ψ_(s) and theapplied gate voltage V_(GS), and the variable n quantifies the couplingcapacitance between the drain-source current I_(DS) and the surfacepotential ψ_(s). A conventional Boltzmann-limited FET, such as a planarFET or fin-FET, has characteristics of m>1 and n=60, whereas a SS-FEThaving an integrated BRS fabricated as described with respect to one ormore embodiments exhibits m>1 and n<60. As a result, the SS-FET exhibitsa subthreshold switching slope of less than the fundamental Boltzmannlimit of 60 millivolts per decade at room temperature by harnessing theabrupt resistance switch of the BRS integrated in series with the sourceor drain of the conventional MOSFET.

With reference to FIGS. 2A-2B, these figures depict example conventionalMOSFET structures at MOL and BEOL stages of semiconductor fabrication.FIG. 2A depicts an example conventional MOSFET structure at a MOL stageof semiconductor fabrication including a silicon substrate (Si) having anumber of fins and a shallow trench isolation (STI) layer disposed onthe substrate. Source/drain (S/D) contacts (CA) are formed over metallictrench contacts (TS), and the trench contacts (TS) are in contact withS/D regions (Epitaxy) disposed between the fins. A gate contact (CB) isformed in contact with a gate region. A nitride cap covers portions ofthe gate regions. An insulating side wall is formed around the gateregions as spacers (typically, of low-K materials) to electricallyisolate the gate region from the S/D regions. FIG. 2B depicts an exampleconventional MOSFET structure at a BEOL stage of semiconductorfabrication. As shown in FIG. 2B, metallization layer contacts (MO) overdeposited over and in contact with the S/D contacts (CA) and gatecontact (CB).

With reference to FIGS. 3A-3B, these figures depict embodiments ofSS-FET structures at MOL and BEOL stages of semiconductor fabrication.FIG. 3A depicts an embodiment of a SS-FET structure at an MOL stage ofsemiconductor fabrication. In the embodiment illustrated in FIG. 3A, anIMT material is integrated between a trench contact (TS) and an S/Dcontact (CA) such that the multilayer system created by the S/D contactmaterial, the IMT material, and the trench contact (TS) material createsa reversible switch as further described herein. A bottom portion of S/Dcontact (CA) functions as a top contact (TC) of the reversible switch,and a top portion of trench contact (TS) functions as a bottom contact(BC) of the reversible switch.

FIG. 3B depicts an embodiment of a SS-FET structure at a BEOL stage ofsemiconductor fabrication. In the embodiment illustrated in FIG. 3B, IMTmaterial is integrated between an S/D contact (CA) and a metallizationcontact (M0) such that the multilayer system created by the S/D contact(CA), the IMT material, and the metallization layer contact (M0) createsa reversible switch as further described herein. A bottom portion ofmetallization layer contact (M0) functions as a top contact (TC) of thereversible switch, and a top portion of the S/D contact (CA) functionsas a bottom contact (BC) of the reversible switch.

FIGS. 4-6 depict example operating principles of a Steep-Switch FET(SS-FET) according to one or more embodiments. Referring to FIG. 4, therobust field-effect dynamics of a MOSFET 402 is combined with the steepswitching capabilities of a bi-stable resistive system (BRS) such asinsulator-to-metal transition (IMT) materials or a threshold-switchingselector (TSS). Referring to FIG. 5, the SS-FET exhibits an electricallyinduced abrupt resistivity change due to the BRS. The high-resistivityinsulating state (HRS) of the BRS exponentially reduces the OFF-stateleakage current (I_(OFF)) while the abrupt resistance switching to thelow-resistivity metallic state (LRS) results in negligible reduction inon-state drive current (I_(ON)) of the SS-FET. The SS-FET enables asteep switching slope and enhanced I_(ON)/I_(OFF) ratio overconventional MOSFETs.

With reference to FIG. 6, a SS-FET architecture structure 600 is shownin an OFF state 602, and an ON state 604. In OFF state 602, when the BRSis in the insulating High Resistance State (HRS), the effective gatevoltage of the SS-FET (V_(GS′)) is reduced by the potential drop acrossthe BRS due to the large insulator resistance. As a result, theOFF-state leakage of the MOSFET is exponentially reduced. In ON state604, when BRS is in the metallic Low Resistance State (LRS), theeffective gate voltage of the SS-FET V_(GS′)≈V_(GS) since the potentialdrop across BRS becomes negligible as the metallic state has multipleorders of magnitude lower resistance. As a result, ON-current loss isnegligible. The reversible resistance switch from HRS to LRS can beelectrically triggered for both positive and negative voltage polaritieswhich makes the concept applicable to both nFET and pFET technologies aswell as other compatibility with other CMOS technologies.

With reference to FIG. 7, a symmetrical SS-FET architecture structure700 is shown in an OFF state 702 and an ON state 704. In the embodiment,of FIG. 7, the BRS is integrated on the source and drain. On top ofOFF-state leakage reduction due to source side potential drop, the drainside resistance also significantly reduces the effective drainpotential, i.e. significantly reducing the drain-induced barrierlowering (DIBL) effect on the potential barrier in the channel resultingin a potentially exponential effect on OFF-state leakage reduction. Inaddition, the effective V_(DS) or lateral drift field between source anddrain is reduced, further reducing OFF-state leakage to some extent.With symmetric integration no extra mask is needed to selectively openthe source or drain side after TS formation as both the source and drainBRS may integrated during the trench contact (TS) formation stages.

With reference to FIGS. 8-13, these figures depict an example processfor fabricating a steep-switch field effect transistor in accordancewith an embodiment. In the embodiment illustrated in FIGS. 8-13, an IMTmaterial is asymmetrically integrated as a BRS on either the source ordrain at the trench contact (TS) level such as at a MOL stage offabrication.

With reference to FIG. 8, this figure depicts a portion of the processin which a semiconductor structure 800 is received. Structure 800includes a substrate 802 having a number of fins 804 disposed thereon.In a particular embodiment, substrate 802 and fins 804 are formed of asilicon (Si) material. A shallow trench isolation layer (STI) 806 isdisposed upon substrate 802. Structure 800 includes trenches etched intosubstrate 802 with a source/drain (S/D) 808 formed within the trenchesadjacent to fins 804. In a particular embodiment, the trenches areformed by a reactive ion etching (RIE) process. In particularembodiments, S/D 808 is formed by an epitaxial growth process. Gates 810are formed on fins 804 and covered by a nitride cap 812.

With reference to FIG. 9, this figure depicts another portion of aprocess in which a structure 900 is formed. The fabrication systemperforms a trench contact metallization process to form trench contacts(TS) 814 within the trenches upon S/D 808 by depositing trench contactmetal on S/D 808. In the particular embodiment, the fabrication systemfurther performs a chemical mechanical planarization (CMP) process toplanarize the surface of structure 900.

With reference to FIG. 10, this figure depicts another portion of aprocess in which a structure 1000 is formed. The fabrication systemapplies an organic planarization layer (OPL) 816 to mask portions ofstructure 900 and performs recess patterning on the middle trenchcontact (TS) 814 to etch a portion of trench contact (TS) to form arecess therein below a top surface of nitride cap 812.

With reference to FIG. 11, this figure depicts another portion of aprocess in which a structure 1100 is formed. The IMT material 818 isdeposited within the recess in contact with trench contact 814 and anupper surface of structure 1000 of FIG. 10. In one or more embodiments,IMT material 818 can be deposited using conventional depositiontechniques such as but not limited to Sputtering, chemical vapordeposition (CVD), atomic layer deposition (ALD), or any other suitabledeposition process. In particular embodiments, the deposition of IMTmaterial 818 can also be followed by an annealing process such as RapidThermal Processing (RTP) to re-crystallize the material if required toachieve the desired IMT properties.

With reference to FIG. 12, this figure depicts another portion of aprocess in which a structure 1200 is formed. In the embodiment, thefabrication system planarizes IMT material 818 using a CMP process toremove IMT material 818 except for the portions of IMT material 818deposited within the recess.

With reference to FIG. 13, this figure depicts another portion of aprocess in which a structure 1300 is formed. In the embodiment, thefabrication forms a S/D contact (CA) 820 upon IMT material 818 to formBC/IMT/TC reversible switch 824. A bottom portion of S/D contact (CA)functions as a top contact (TC) of reversible switch 824, and a topportion of trench contact (TS) 814 functions as a bottom contact (BC) ofreversible switch 824. In the embodiment, a gate contact (CB) 822 isfurther deposited upon a gate 810. Accordingly, a steep-switch fieldeffect transistor (SS-FET) is fabricated in accordance with anembodiment.

With reference to FIGS. 14-20, these figures depict another exampleprocess for fabricating a steep-switch field effect transistor inaccordance with an embodiment. In the embodiment illustrated in FIGS.14-20, a fabrication system (not shown) asymmetrically integrates an IMTmaterial as a BRS on either the source or drain at the S/D contact (CA)level such as at a BEOL stage of fabrication. In one or moreembodiments, integration at the BEOL state is not limited to between S/Dcontact (CA) and metallization contacts (M0) fabrication levels. Inparticular embodiments, IMT material can also be integrated betweenM_(n) and M_(n+1) levels using the same or a similar process sequence.

With reference to FIG. 14, this figure depicts a portion of a process inwhich a semiconductor structure 1400 is received. Structure 1400includes a substrate 1402 having a number of fins 1404 disposed thereon.In a particular embodiment, substrate 1402 and fins 1404 are formed of asilicon (Si) material. A shallow trench isolation layer (STI) 1406 isdisposed upon substrate 1402. Structure 1400 includes trench contacts(TS) 1414 in contact with a source/drain (S/D) 1408 adjacent to fins1404. Gates 1410 are formed on fins 1404 and covered by a nitride cap1412. S/D contacts (CA) 1416 are formed on trench contacts (TS) 1414,and a gate contact (CB) 1418 is formed on gate 1410.

With reference to FIG. 15, this figure depicts another portion of aprocess in which a structure 1500 is formed. The fabrication systemapplies an OPL 1420 to mask portions of structure 1400 and performsrecess patterning on the S/D contact (CA) 1416 to selectively etch aportion of S/D contact (CA) to form a recess 1422 therein.

With reference to FIG. 16, this figure depicts another portion of aprocess in which a structure 1600 is formed. In the embodiment, thefabrication system deposits IMT material 1424 within recess 1422 incontact with S/D contact (CA) 1416 and an upper surface of structure1500 of FIG. 15. In one or more embodiments, IMT material 1424 can bedeposited using conventional deposition techniques such as but notlimited to Sputtering, chemical vapor deposition (CVD), atomic layerdeposition (ALD), or any other suitable deposition process. Inparticular embodiments, the deposition of IMT material 1424 can also befollowed by an annealing process such as Rapid Thermal Processing (RTP)to re-crystallize the material if required to achieve the desired IMTproperties.

With reference to FIG. 17, this figure depicts another portion of aprocess in which a structure 1700 is formed. In the embodiment, thefabrication system planarizes IMT material 1424 using a CMP process toremove IMT material 1424 except for the portions of IMT material 1424deposited within recess 1422.

With reference to FIG. 18, this figure depicts another portion of aprocess in which a structure 1800 is formed. In the embodiment, thefabrication system deposits an insulation cap layer (NBLOCK cap) 1426 ona top surface of the structure 1700 of FIG. 17. In one or moreembodiments, the insulation cap layer 1426 functions to protect themetals underneath that can be easily damaged or oxidized.

With reference to FIG. 19, this figure depicts another portion of aprocess in which a structure 1900 is formed. In the embodiment, thefabrication system deposits a dielectric layer 1428 upon a top surfaceof insulation cap layer (NBLOCK cap) 1426.

With reference to FIG. 20, this figure depicts another portion of aprocess in which a structure 2000 is formed. In the embodiment, thefabrication system deposits metallization contacts (M0) 1430 such thatthe multilayer system created by the S/D contact (CA) 1416, the IMTmaterial 1424, and the metallization layer contact (M0) 1430 creates areversible switch 1432. A bottom portion of metallization layer contact(M0) 1430 functions as a top contact (TC) of reversible switch 1432, anda top portion of S/D contact (CA) 1416 functions as a bottom contact(BC) of reversible switch 1432. The fabrication system furtherplanarizes metallization layer contact (M0) 1430 using a CMP process.Accordingly, a steep-switch field effect transistor (SS-FET) isfabricated in accordance with an embodiment.

With reference to FIGS. 21-27, these figures depict another exampleprocess for fabricating a steep-switch field effect transistor inaccordance with an embodiment. In the embodiment illustrated in FIGS.21-27, a fabrication system (not shown) asymmetrically integrates aThreshold-Switching Selector (TSS) as a BRS on either the source ordrain at the trench contact (TS) level such as at a MOL stage offabrication.

With reference to FIG. 21, this figure depicts a portion of the processin which a semiconductor structure 2100 is received. Structure 2100includes a substrate 2102 having a number of fins 2104 disposed thereon.In a particular embodiment, substrate 2102 and fins 2104 are formed of asilicon (Si) material. A shallow trench isolation layer (STI) 2106 isdisposed upon substrate 2102. Structure 2100 includes trenches etchedinto substrate 2102 with a source/drain (S/D) 2108 formed within thetrenches adjacent to fins 2104. In a particular embodiment, the trenchesare formed by a RIE process. In particular embodiments, S/D 2108 isformed by an epitaxial growth process. Gates 2110 are formed on fins2104 and covered by a nitride cap 2112.

With reference to FIG. 22, this figure depicts another portion of aprocess in which a structure 2200 is formed. The fabrication systemperforms a trench contact metallization process to form trench contacts(TS) 2114 within the trenches upon S/D 2108 by depositing trench contactmetal on S/D 2108. In the particular embodiment, the fabrication systemfurther performs a chemical mechanical planarization (CMP) process toplanarize the surface of structure 2200.

With reference to FIG. 23, this figure depicts another portion of aprocess in which a structure 2300 is formed. The fabrication systemapplies an OPL 2116 to mask portions of structure 2300 and performsrecess patterning to selectively open the trench contact (TS) 2114, tofurther etch a portion of trench contact (TS) 2114 and to form a recesstherein below a top surface of nitride cap 2112.

With reference to FIG. 24, this figure depicts another portion of aprocess in which a structure 2400 is formed. The fabrication systemstrips OPL 2116 and deposits a conformal TRS oxide layer 2118 within therecess in contact with trench contact 2114 and an upper surface ofstructure 2300 of FIG. 23. In the embodiment, TRS oxide layer 2118 hostsa volatile metallic filament driving the reversible switching behavior.In other embodiments, the oxide layer can be replaced with othersuitable dielectric materials.

With reference to FIG. 25, this figure depicts another portion of aprocess in which a structure 2500 is formed. In the embodiment, thefabrication system deposits a TRS top electrode (TE) metallization layer2120 upon the TRS oxide layer 2118 forming a top electrode (TE) withinthe recess upon TRS oxide layer 2118.

With reference to FIG. 26, this figure depicts another portion of aprocess in which a structure 2600 is formed. In the embodiment, thefabrication system removes TRS top electrode (TE) metallization layer2120 except for the portion of TRS top electrode (TE) metallizationlayer 2120 deposited within the recess. In the embodiment, a TSS 2122 isformed by the interface between TRS top electrode (TE) metallizationlayer 2120, TRS oxide layer 2118, and trench contact 2114.

With reference to FIG. 27, this figure depicts another portion of aprocess in which a structure 2700 is formed. In the embodiment, a S/Dcontact (CA) 2124 is formed upon TRS top electrode (TE) metallizationlayer 2120. In the embodiment, a gate contact (CB) 2126 is furtherdeposited upon gate 2110. Accordingly, a steep-switch field effecttransistor (SS-FET) is fabricated in accordance with an embodiment.

With reference to FIGS. 28-35, these figures depict another exampleprocess for fabricating a steep-switch field effect transistor inaccordance with an embodiment. In the embodiment illustrated in FIGS.28-35, a fabrication system asymmetrically integrates athreshold-switching selector (TSS) as a BRS on either the source ordrain at the S/D contact (CA) level such as at a BEOL stage offabrication. In one or more embodiments, integration at the BEOL stateis not limited to between S/D contact (CA) and metallization contacts(M0) fabrication levels. In particular embodiments, IMT material canalso be integrated between M_(n) and M_(n+1) levels using the same or asimilar process sequence.

With reference to FIG. 28, this figure depicts a portion of a process inwhich a semiconductor structure 2800 is received. Structure 2800includes a substrate 2802 having a number of fins 2804 disposed thereon.In a particular embodiment, substrate 2802 and fins 2804 are formed of asilicon (Si) material. A shallow trench isolation layer (STI) 2806 isdisposed upon substrate 2802. Structure 2800 includes trench contacts(TS) 2814 in contact with a source/drain (S/D) Epitaxy 2808 adjacent tofins 2804. Gates 2810 are formed on fins 2804 and covered by a nitridecap 2812. S/D contacts (CA) 2816 are formed on trench contacts (TS)2814, and a gate contact (CB) 2818 is formed on gate 2810.

With reference to FIG. 29, this figure depicts another portion of aprocess in which a structure 2900 is formed. The fabrication systemapplies an OPL 2820 to mask portions of structure 2900 and performsrecess patterning on the S/D contact (CA) 2816 to etch a portion of S/Dcontact (CA) 2816 to form a recess 2822 therein.

With reference to FIG. 30, this figure depicts another portion of aprocess in which a structure 3000 is formed. In the embodiment, thefabrication system deposits a conformal TRS oxide layer 2824 withinrecess 2822 in contact with S/D contact (CA) 2816 and an upper surfaceof structure 2900 of FIG. 29. In the embodiment, TRS oxide layer 2118hosts a volatile metallic filament driving the reversible switchingbehavior. In other embodiments, the oxide layer can be replaced withother suitable dielectric materials.

With reference to FIG. 31, this figure depicts another portion of aprocess in which a structure 3100 is formed. In the embodiment, thefabrication system deposits a TRS top electrode (TE) metallization layer2826 upon the TRS oxide layer 2824 forming a top electrode (TE) withinthe recess.

With reference to FIG. 32, this figure depicts another portion of aprocess in which a structure 3200 is formed. In the embodiment, thefabrication system removes TRS top electrode (TE) metallization layer2826 except for the portion of TRS top electrode (TE) metallizationlayer 2826 deposited within the recess. In the embodiment, a TSS 2828 isformed by the interface between TRS top electrode (TE) metallizationlayer 2824, TRS oxide layer 2824, and S/D contact (CA) 2816.

With reference to FIG. 33, this figure depicts another portion of aprocess in which a structure 3300 is formed. In the embodiment, thefabrication system deposits an insulation cap layer (NBLOCK cap) 2830 ona top surface of the structure 3200 of FIG. 32. In one or moreembodiments, the insulation cap layer 2830 functions to protect themetals underneath that can be easily damaged or oxidized.

With reference to FIG. 34, this figure depicts another portion of aprocess in which a structure 3400 is formed. In the embodiment, thefabrication system deposits a dielectric layer 2832 upon a top surfaceof insulation cap layer (NBLOCK cap) 2830.

With reference to FIG. 35, this figure depicts another portion of aprocess in which a structure 3500 is formed. In the embodiment, thefabrication system deposits metallization contacts (M0) 2834 in contactwith TSS 2828. Accordingly, a steep-switch field effect transistor(SS-FET) is fabricated in accordance with an embodiment.

With reference to FIGS. 36-41, these figures depict another exampleprocess for fabricating a steep-switch field effect transistor inaccordance with an embodiment. In the embodiment illustrated in FIGS.36-41, a fabrication system (not shown) symmetrically integrates an IMTmaterial as a BRS on either the source or drain at the trench contact(TS) level such as at a MOL stage of fabrication.

With reference to FIG. 36, this figure depicts a portion of the processin which a semiconductor structure 3600 is received. Structure 3600includes a substrate 3602 having a number of fins 3604 disposed thereon.In a particular embodiment, substrate 3602 and fins 3604 are formed of asilicon (Si) material. A shallow trench isolation layer (STI) 3606 isdisposed upon substrate 3602. Structure 3600 includes trenches etchedinto substrate 802 with source/drain (S/D) 3608 formed within thetrenches adjacent to fins 3604. In a particular embodiment, the trenchesare formed by an RIE process. In particular embodiments, S/D 3608 isformed by an epitaxial growth process. Gates 3610 are formed on fins3604 and covered by a nitride cap 3612.

With reference to FIG. 37, this figure depicts another portion of aprocess in which a structure 3700 is formed. The fabrication systemperforms a trench contact metallization process to form trench contacts(TS) 3616 within the trenches upon S/D 3608 by depositing trench contactmetal on S/D 3608. In the particular embodiment, the fabrication systemfurther performs a chemical mechanical planarization (CMP) process toplanarize the surface of structure 3700.

With reference to FIG. 38, this figure depicts another portion of aprocess in which a structure 3800 is formed. The fabrication systemrecesses the trench contacts (TS) 3616 without requiring patterning toremove a portion of trench contacts (TS) 3616 to form recesses 3618therein below the top surface of nitride cap 3612.

With reference to FIG. 39, this figure depicts another portion of aprocess in which a structure 3900 is formed. The fabrication systemdeposits IMT material 3620 within each of the recesses 3618 in contactwith trench contacts (TS) 3616 and an upper surface of structure 3800 ofFIG. 38. In one or more embodiments, IMT material 3620 can be depositedusing conventional deposition techniques such as but not limited toSputtering, chemical vapor deposition (CVD), atomic layer deposition(ALD), or any other suitable deposition process. In particularembodiments, the deposition of IMT material 3620 can also be followed byan annealing process such as Rapid Thermal Processing (RTP) tore-crystallize the material if required to achieve the desired IMTproperties.

With reference to FIG. 40, this figure depicts another portion of aprocess in which a structure 4000 is formed. In the embodiment, thefabrication system planarizes IMT material 3620 using a CMP process toremove IMT material 3620 except for the portions of IMT material 3620deposited within the recesses 3618.

With reference to FIG. 41, this figure depicts another portion of aprocess in which a structure 4100 is formed. In the embodiment, a S/Dcontact (CA) 3622 is formed upon IMT material 3620 to form BC/IMT/TCreversible switch 3626. A bottom portion of S/D contact (CA) 3622functions as a top contact (TC) of reversible switch 3626, and a topportion of trench contact (TS) 3616 functions as a bottom contact (BC)of reversible switch 3626. In the embodiment, a gate contact (CB) 3624is further deposited upon a gate 3610. Accordingly, a steep-switch fieldeffect transistor (SS-FET) is fabricated in accordance with anembodiment.

With reference to FIG. 42, this figure depicts a flowchart of an exampleprocess 4200 for fabricating a steep-switch field effect transistor inaccordance with an illustrative embodiment. In the embodimentillustrated in FIG. 42, a fabrication system (not shown) integratesbi-stable resistive system (BRS) on either the source or drain at thetrench contact (TS) level such as at a MOL stage of fabrication.

In block 4202, the fabrication system receives a semiconductor structureincluding a substrate, a fin disposed on the substrate, a source/draindisposed on the substrate adjacent to the fin, a gate disposed upon thefin, a cap disposed on the gate, and a trench extending to thesource/drain.

In block 4204, the fabrication system forms a trench contact in thetrench in contact with the source/drain. In block 4206, the fabricationsystem forms a recess in a portion of the trench contact below a topsurface of the cap using a recess patterning process. In block 4208, thefabrication system forms a bi-stable resistive system (BRS) in therecessed portion of the trench contact. In particular embodiments, thefabrication system deposits a BRS material in the recessed portion ofthe trench contact. In a particular embodiment, the BRS materialincludes an insulator-to-metal transition (IMT) material. In anotherparticular embodiment, the BRS material includes a threshold-switchingselector.

In block 4210, the fabrication system forms a source/drain contact uponthe BRS material, a portion of the trench contact, the BRS material, anda portion of the source/drain contact forming a reversible switch. Theprocess 4200 then ends. Accordingly, a steep-switch field effecttransistor (SS-FET) is fabricated in accordance with an embodiment.

With reference to FIG. 43, this figure depicts a flowchart of anotherexample process 4300 for fabricating a steep-switch field effecttransistor in accordance with an illustrative embodiment. In theembodiment illustrated in FIG. 43, a fabrication system (not shown)integrates a bi-stable resistive system (BRS) material on either thesource or drain at the S/D contact (CA) level such as at a BEOL stage offabrication. In one or more embodiments, integration at the BEOL stateis not limited to between S/D contact (CA) and metallization contacts(M0) fabrication levels. In particular embodiments, IMT material canalso be integrated between M_(n) and M_(n+1) levels using the same or asimilar process sequence.

In block 4302, the fabrication system receives a semiconductor structureincluding a substrate, a fin disposed on the substrate, a source/draindisposed on the substrate adjacent to the fin, a gate disposed upon thefin, a cap disposed on the gate, a trench contact formed on and incontact with the source/drain; and a source/drain contact formed on anin contact with the trench contact. In block 4304, the fabricationsystem forms a recess in a portion of the source/drain contact using arecess patterning process.

In block 4306, the fabrication system forms a bi-stable resistive system(BRS) in the recessed portion of the source/drain contact. In a one ormore embodiments, the fabrication system deposits a BRS material in therecessed portion of the source/drain contact. In a particularembodiment, the BRS material includes an insulator-to-metal transition(IMT) material. In another particular embodiment, the BRS materialincludes a threshold-switching selector.

In block 4308, the fabrication system forms a metallization layercontact upon the BRS material. In the embodiment, a portion of thesource/drain contact, the BRS material, and a portion of themetallization layer contact forms a reversible switch. The process 4300then ends. Accordingly, a steep-switch field effect transistor (SS-FET)is fabricated in accordance with an embodiment.

Thus, a computer implemented method, system or apparatus, and computerprogram product are provided in the illustrative embodiments forfabricating SS-FETs and other related features, functions, oroperations. Where an embodiment or a portion thereof is described withrespect to a type of device, the computer implemented method, system orapparatus, the computer program product, or a portion thereof, areadapted or configured for use with a suitable and comparablemanifestation of that type of device.

Where an embodiment is described as implemented in an application, thedelivery of the application in a Software as a Service (SaaS) model iscontemplated within the scope of the illustrative embodiments. In a SaaSmodel, the capability of the application implementing an embodiment isprovided to a user by executing the application in a cloudinfrastructure. The user can access the application using a variety ofclient devices through a thin client interface such as a web browser(e.g., web-based e-mail), or other light-weight client-applications. Theuser does not manage or control the underlying cloud infrastructureincluding the network, servers, operating systems, or the storage of thecloud infrastructure. In some cases, the user may not even manage orcontrol the capabilities of the SaaS application. In some other cases,the SaaS implementation of the application may permit a possibleexception of limited user-specific application configuration settings.

The present invention may be a system, a method, and/or a computerprogram product at any possible technical detail level of integration.The computer program product may include a computer readable storagemedium (or media) having computer readable program instructions thereonfor causing a processor to carry out aspects of the present invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, configuration data for integrated circuitry, oreither source code or object code written in any combination of one ormore programming languages, including an object oriented programminglanguage such as Smalltalk, C++, or the like, and procedural programminglanguages, such as the “C” programming language or similar programminglanguages. The computer readable program instructions may executeentirely on the user's computer, partly on the user's computer, as astand-alone software package, partly on the user's computer and partlyon a remote computer or entirely on the remote computer or server. Inthe latter scenario, the remote computer may be connected to the user'scomputer through any type of network, including a local area network(LAN) or a wide area network (WAN), or the connection may be made to anexternal computer (for example, through the Internet using an InternetService Provider). In some embodiments, electronic circuitry including,for example, programmable logic circuitry, field-programmable gatearrays (FPGA), or programmable logic arrays (PLA) may execute thecomputer readable program instructions by utilizing state information ofthe computer readable program instructions to personalize the electroniccircuitry, in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the blocks may occur out of theorder noted in the Figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

What is claimed is:
 1. A method for fabricating a steep-switchtransistor, comprising: receiving a semiconductor structure including asubstrate, a fin disposed on the substrate, a source/drain disposed onthe substrate adjacent to the fin, a gate disposed upon the fin, a capdisposed on the gate, a trench contact formed on and in contact with thesource/drain; and a source/drain contact formed on an in contact withthe trench contact; forming a recess in a portion of the source/draincontact using a recess patterning process; depositing a bi-stableresistive system (BRS) material in the recess in contact with theportion of the source/drain contact; and forming a metallization layercontact upon the BRS material, a portion of the source/drain contact,the BRS material, and a portion of the metallization layer contactforming a reversible switch.
 2. The method of claim 1, wherein formingthe recess in the portion of the trench contact further comprises:applying an organic planarization layer (OPL) to mask portions ofsemiconductor structure; etching a portion of the source/drain contactto form the recess therein; and removing the OPL.
 3. The method of claim1, wherein the BRS material comprises an insulator-to-metal transition(IMT) material.
 4. The method of claim 3, wherein depositing the BRSmaterial in the recess includes depositing the IMT material in contactwith the portion of the source/drain contact.
 5. The method of claim 4,further comprising: removing a portion of the IMT material outside ofthe recess using a planarization process.
 6. The method of claim 5,wherein the planarization process includes a chemical mechanicalplanarization (CMP) process.
 7. The method of claim 1, wherein the BRSmaterial comprises a threshold-switching selector.
 8. The method ofclaim 7, wherein depositing the BRS material in the recess comprises:depositing an oxide layer within the recess; and forming a top electrodewithin the recess upon the oxide layer.
 9. The method of claim 1,further comprising: applying an insulation cap layer to the structure;and depositing a dielectric layer upon the insulation layer, themetallization layer contact being formed through the insulation caplayer and the dielectric layer.